Re: Named parameters in make?

[Lane Schwartz]

On Fri, Jun 10, 2011 at 11:19 AM, Philip Guenther <address@hidden>wrote:

> On Fri, Jun 10, 2011 at 6:09 AM, Lane Schwartz <address@hidden> wrote:
> > A major reason why the resulting code looks cryptic is because of the $1,
> > $2, $3... variable names for parameters. If there were some way to name
> > these parameters, the resulting code would be better documented and more
> > readable.
> ...
> > Here's a (slightly simplified) use case that comes from one of my
> Makefiles:
> >
> > TMs:=$(wildcard tm-*)
> > LMs:=$(wildcard lm-*)
> > DEVs:=$(wildcard dev-*)
> >
> > define OPTIMIZE
> >
> > $1.$2.$3/optimize.cfg: $1/fragment.cfg $2/fragment.cfg $3/fragment.cfg |
> $1.$2.$3
> >      cat $$^ > $$@
> >
> > $1.$2.$3:
> >      mkdir -p $$@
> >
> > endef
> >
> > # Dynamically construct new targets
> > $(foreach TM,${TMs},\
> >   $(foreach LM,${LMs},\
> >      $(foreach DEV,${DEVs},\
> >         $(eval $(call OPTIMIZE,${TM},${LM},${DEV}))\
> >      )\
> >   )\
> > )
> >
> >
> > Named parameters would in this case mean that I could use names like
> ${TM}
> > instead of $1, ${LM} instead of $2, and ${DEV} instead of $3, making the
> > define block more readable.
>
> You *can* use those names, Right Now!  You're setting TM, LM, and DEV
> right now to exactly the value you want.  You don't *have* to use $1,
> $2, and $3.  Indeed, if you don't then you don't need to use $(call)
> here at all; that's (almost) all that $(call) does, compared to simply
> expanding the named variable.  Compare:
>
> -----
> TMs:=$(wildcard tm-*)
> LMs:=$(wildcard lm-*)
> DEVs:=$(wildcard dev-*)
>
> define OPTIMIZE
>
> all: ${TM}.${LM}.${DEV}/optimize.cfg
> ${TM}.${LM}.${DEV}/optimize.cfg: ${TM}/fragment.cfg ${LM}/fragment.cfg \
>                        ${DEV}/fragment.cfg | ${TM}.${LM}.${DEV}
>        cat $$^ > $$@
>
> ${TM}.${LM}.${DEV}:
>        mkdir -p $$@
>
> endef
>
> # Dynamically construct new targets
> $(foreach TM,${TMs},\
>  $(foreach LM,${LMs},\
>     $(foreach DEV,${DEVs},\
>        $(eval ${OPTIMIZE})\
>     )\
>  )\
> )
> ----
>
Wow. This is incredible! Thank you, Philip!!! I consider myself to be a
pretty savvy make user, but I did not know about this feature.

Paul, this needs to be documented. The sections in the manual on call and
eval don't talk to this point at all. It seems that an example like this
should go in the eval section.

I think it's very interesting that within the define block, using the origin
function on the parameters (TM, LM, DEV) reports that they are automatic
variables. This should also be documented (that the var of a foreach is
considered to be an automatic variable while it's in scope).

Paul, if you want a volunteer for adding this info to the manual, let me
know. :)

Cheers,
Lane